Megan Fox and Shia LaBeouf flee destruction in "Transformers: Revenge of the Fallen."

Director Michael Bay suggested his film should not be seriously questioned.

"It's called summer fun. It's a robot movie," Bay said.

Don't tell that to the fanboys who've waited two years for the "Transformers" sequel, or to Steven Spielberg's DreamWorks and Paramount Pictures, who hope it will top the $700 million the first movie made.

The newest Transformers production is a marvel of moviemaking technology that combines record-setting practical effects -- real explosions and stunts -- with unrivaled computer-generated action.

Star Autobot Optimus Prime appears life-sized on an IMAX screen in one battle.

The movie is so big and action-packed, though, that more than one reviewer emerged from an IMAX screening last week talking about how it was tough to tell who was fighting who in some scenes. A guide to the Autobots and Decepticons »

Producer Lorenzo di Bonaventura noted in an interview that "the action scenes are only as good as the audience is invested in the character."

"So, if they're not invested in the character, then the action is just a lot of noise," he said.

In the new film, which takes place two years after "Transformers," LaBeouf's Sam Witwicky is at college, trying to get his life back to normal. But the Transformers -- the good Autobots and the evil Decepticons -- have different ideas. As the robots battle over the AllSpark, a life-giving energy for Transformers, humans are caught in the middle, with the planet at risk.

But humans are only part of the story. Those characters Bay wants you to care about include 46 robots -- 32 more than in the last film.

These Autobots and Decepticons were farm-raised -- on a computer server farm owned by Industrial Light & Magic. Their simulations took up seven times more computer disk space than in the first movie.

The job of "rendering" the largest -- a 10-story-tall sand-plowing machine of destruction named Devastator -- caused a computer to explode, according to visual effects supervisor Scott Farrar. "Little puffs of smoke, just like in the movie," Farrar said.

Filming was very physical -- and dangerous -- for the human actors, because Bay balanced his computer simulations with a big dose of reality.

Actor Ramon Rodriguez said he "popped a shoulder, which was a lot of fun," filming a scene in which the Devastator is plowing through a desert, with fans blowing a 100 mph wind into his face.

"So, I had sand, soot, dirt blowing in my face and I had two guys behind me with wires attached to my ankles pulling me," Rodriguez said. "Not enough yet. We need cars flipping over my head. So, he brought two cars and he literally had them attached to a hydraulic crane, flip inches above my head. So, the guys were yanking, you know, on the cables on my ankles and, yeah, on one of the takes my shoulder popped out and we continued rolling."

"That was the shot we used," Bay said.

"That was probably the shot you used and thank you, Mike, it was great," Rodriguez said.

LaBeouf suffered a serious hand injury in a car crash away from the set that almost derailed production, until Bay ordered his star a transparent Kevlar cast

"The problem was if he jammed his fingers, he could lose his fingers forever, so we had experts of the world come up with this design," Bay said.

After shutting down production for just a day, Bay found a way to work LaBeouf's hurt hand into the story.

Megan Fox, who reprised her role as LaBeouf's girlfriend, said the cast "drank a lot" to relax after 16-hour days on the set. Bay insisted shoots were limited to 12-hour days.

Action scenes meant the actors had to do a lot of running -- much of it through desert sand in Jordan and Egypt.

Many of their sprints were through real blasts, including one that landed in the Guinness Book of World Records.

"We made history, the biggest practical explosion in the history of filmmaking that included the actors," said Tyrese Gibson, who played a U.S. Air Force sergeant.

The blasts, military hardware and Fox, featured in short pants in the sexy opening sequence, should appeal to the teenage boys in the theater.

"We got that first shot out of the way, just to get it out for the young boys and move on," Bay said.

The first "Transformers" broke box office records two years ago by drawing a broad audience, including adult women.

Bay said there's still plenty for the ladies -- especially with the romantic relationship between LeBeouf and Fox.

"What's making this accessible to everybody is the humor in it, and I think that's how you make it accessible to everybody," Bay said. "It's not just for the fanboys."

The humor, though, has aged with the characters. The script includes plenty of dog-humping and testicular sight gags.

"Transformers: Revenge of the Fallen" received a PG-13 rating "for intense sequences of sci-fi action violence, language, some crude and sexual material, and brief drug material."

The second Transformers movie runs 140 minutes, three minutes shorter than the first.